With increasingly higher resolution of camera modules in recent years, there are growing demands for a mounting technique that allows highly precise adjustment of a relative positional relationship between an imaging lens and an image pickup device.
Conventional techniques are known for adjusting a relative positional relationship between an imaging lens and an image pickup device with reference to an outline and an appearance of the camera module. As an example, Patent Literature 1 discloses a technique of capturing an image of an actuator with use of an imaging device and adjusting a relative positional relationship between an optical axis of an imaging lens and a center of an image pickup device on the basis of a gloss, a color, and the image of the actuator.
However, there have recently been growing demands for positional adjustment with precision higher than positional adjustment with reference to the outline and the appearance of a camera module as disclosed in Patent Literature 1.
Patent Literature 2 discloses a technique of (i) providing a camera module body in an adjustment frame, (ii) adjusting the position of the camera module body on the basis of an image signal of a test image pickup device which image signal has been obtained from the camera module body, and (iii) bonding and fixing, to the adjustment frame, the camera module body whose position has been adjusted.
Patent Literature 3 discloses a technique of capturing an image of a measurement chart and adjusting a relative positional relationship between an imaging lens and an image pickup device on the basis of positional information of a mark in the image captured. Patent Literature 3 discloses that orientation of the image pickup device is controlled through capture of an image of the measurement chart with use of a reference lens and the image pickup device, while orientation of the image pickup device is controlled through capture of an image of the measurement chart with use of the imaging lens and a reference image pickup device.
The respective techniques disclosed in Patent Literatures 2 and 3 both use an image signal for the purpose of adjusting the relative positional relationship between an imaging lens and an image pickup device. However, the techniques each require an image pickup device not to be mounted on a camera module as a finished product. As a result, the respective techniques disclosed in Patent Literatures 2 and 3 may complicate a process of manufacturing the camera module. The complication of the process of manufacturing the camera module may cause an error in the relative positional relationship between an imaging lens and an image pickup device (to be mounted on a camera module as a finished product) when the image pickup device is mounted on the imaging lens.
In view of the risk, there have been known techniques for directly adjusting a relative positional relationship between an imaging lens and an image pickup device while capturing an image with use of only an image pickup device to be mounted in a camera module as a finished product. Such techniques are disclosed in Patent Literatures 4 and 5, for example.
Patent Literature 4 discloses a technique of obtaining an imaging signal for each of a plurality of measurement positions set along an optical axis of an imaging lens while moving the imaging lens to the measurement positions, and for automatically adjusting, on the basis of the imaging signals, (i) the position of the image pickup device in the optical axis direction and (ii) respective slopes of two axes intersecting with the optical axis at right angles.
Patent Literature 5 discloses a technique for quantitatively detecting the slope of an image pickup device on the basis of data on a plurality of images captured, with use of a fixed image pickup device, of a measurement chart moving along an optical axis of the imaging lens.
Both of the respective techniques disclosed in Patent Literatures 4 and 5 adjust the slope of an image surface of an imaging lens with high precision. Therefore, the techniques each allow high-precision adjustment suitable for the configuration of the camera module.